Sound-projecting apparatus and method



Dec. 18 1923.

E. GRISSINGER SOUND PROJECTING APPARATUS AND METHOD Filed July 12, 19214 Sheets-Sheet 1 31 vwento'q Dec. 18, 1923.

E. GRISSINGER SOUND PROJECTING APPARATUS AND METHOD Filed July 12, 19214 Sheets-Sheet 2 ffoot' maentoz 25 y Y M duh/17f g3, W Aw; arrow;

Dec. 18 1923.

E. GRISSINGER v SOUND PROJECTING APPARATUS AND METHOD Filed July 12,1921 4 Sheets-Sheet 5 31 nuemifoz Ell/mm dizzy/17y afhnnc 1.:

Dec. 18, 1923.

E. GRISSINGER SOUND PROJECTING APPARATUS AND METHOD Filed July 12, 19214 Sheets-Sheet 4 5] nvemtoz will" M arcane:-

Patented Dec. 18, 1923.

PATENT OFFICE.

ELWOOD GRISSINGER, OF BUFFALO, NEW YORK.

SOUND-PROJECTING APPARATUS AND METHOD.

Application filed July 12, 1921.

To all whom it may concern:

Be it known that I, ELWOOD GRIssINGnR,

a citizen of the United States and resident of Buffalo, in the county ofErie and State I of New York, have invented certain new and usefulImprovements in Sound-Projecting Apparatus and Methods, of which thefollowing is a specification.

My present invention is shown as embodied in a phonograph cabinet and itincludes a special form of sound projector peculiarly adapted to servethe purpose of an amplifier for such cabinets, but certain features ofthe projector will be found useful in connection with telephonereceivers and other vibratory diaphragm sound producers and also inconnection with other sources of sound, particularly Where, as in thecase of human speech and music, the sounds com- 20 prise a wide range offrequencies, and particularly where it is desired to faithfullyreproduce a multiplicity of sets of waves or complex waves of manyfrequencies, simultaneously.

A primary object of my invention is to provide an air column associatedat one end with the diaphragm of the phonograph reproducer and at theother end communicating with the open air, in which the air column willbe a suitable medium for development, expansion of wave front, andproject ing into the open air, sound waves having a wide range ofphysical" lengths, including sound waves of which the quarter wavelength is long and requires great length of air column, and also shortwaves of the higher frequencies; the quarter lengths of which may be twoinches or less.

In the ordinary commercial tone arm, the diameter of the air column ismall as compared with the half or quarter wave lengths of the higherfrequencies necessary for good phonographic reproduction and it seems tohe a fact that under such ccndh tions the waves travel around bends andpast obstructions with very iittle detriment.

lVe know from the actual physical lengths of the waves that in suchnarrow conduit the phase conditions of rarification, condensatlon andoscillation at any one instant Serial No. 484,240.

must be nearly the same for regions in advance of the bend, at'the'bend, and'beyond the bend. That is to say, the total phasedifferencesubject to disturbance is small. Hence, such cross-flow,eddying flank diffusion or reflection as can occur around the bends arerelatively innocuous. It is equally evident however, that where thediameter of the conduit is great as compared with the physical length ofthe wave phases. sound energy diffusing or flowing around the shorterinside of the curve may be completely out of phase with correspondingenergy reflected or flowing around the longer path defined by the outerwall of the cons duit.

The above will make it easier to understand some aspects of my devicewherein the waves from the tone arm or other source traverse a conduitcomprising a primary expansion portion in which the wave front isafforded guided and limited but rapid ex pansion along lines divergingin one dimension, with little or no expansion or divergence in the otherdimension, thereby forming a relatively thin sound beam, with widelydiverging flanks and deeply curved wave fronts. This beam dischargesthrough a slot-like outlet which the curved wave fronts orwave phasescross at different times and at different angles. The beam thentraverses a secondary expansion por-' tion in which the wave front isafit'orded guided but rapid expansion in-the other dimension, while thedivergent flanks of the beam are deflected inward by non-divergent wallsso that the inturned portions cross each other and cross the mouth ofthe projector at considerable angles.

The primary conduit may be curved to almost any desired extent in thethin direction without danger of serious phase dispiacement for theshort length waves, the reasons being presumably similar to thosesuggested for the case of a curved tonearni, it is to be noted, however,that curvature either of a small diameter pipe or of a thin layerconduit is not a good thing acoustically. Hencain the preferred form ofmy invention, the middle portion of the air coinorm is made fairlystraight (downward for 1 the cabinet type of phonograph), and the wavesare turned abruptly outward through the side of the cabinet, preferablyby high angle reflection, the arrangement being so ordered that the mainbeam preferably crosses. the plane of the vertical mouth of theprojector at a sharp upward angle.

At every point in my air column where the air path of the waves ismodified by sudden change of size or shape of the air column, the actionon the difierent portions of the wave front of each individual wave isnon-simultaneous and the distances, that is, the effective air columnlengths are also substantially diflerent. Consequently, reflex orbackward flow of wave energy is minimized, practically all of the energygets out, and whatever air column resonance there is,'does not causedistortion so far as detectable by the human ear.

Another feature or aspect of my invention concerns the relation of theslender part of the air column with respect to the succeeding portionwhere there is rapid widening in one dimension. In my device the slenderpart of the air column is in the tone arm. This part is, by itselfconsidered, a resonance column of very definite natural frequenciesincluding a fundamental and the usual harmonies of said fundamentalaccording to the well known laws of pipes, open at one end. Fromstructural necessity the length of this pipe in my instrument is thesame as usual, about 12 inches, but in my case, from this point on, theair column is continuous with and merges into a portion whichprogressively and rapidly widens in one dimension while not expanding atall in the other dimension, and preferably converging in said otherdimension. In my device, the one-dimension widening is progressive for alength at least equal vto and preferably greater than the length of thesmall diameter part of the air column.

By thus intimately associating the slender part of the air column whichis in the tone arm, with an equal or greater length and breadth ofwidened air column, the otherwise sharply resonant air column in thetone arm is not so free to resonate by itself in' accordance with itsown dimensions and elasticity.

The composite unit comprising the slender air column in the tone armconjoined with a widened portion having a length equal to i or greaterthan the length of the tone arm tit) tit?

s narrate jecting waves of all lengths. The widened portion may becurved in the direction of its thinness through an arc of 90 degrees ormore, provided the radius of curvature be not too sharp, withoutsubstantial impairment of its function. Consequently it is quitepossible to arrange the outlet slot 'h0'r izontally in the front face ofthe cabinet and have the intermediate conduit curved through 90 degreesto bring its small end into registry with the vertical passage throughwhich the tone arm discharges downward.

The slot outlet however is of special advantage in connection with thereflector outlet shown in the drawings. The thinner the slot the thinneris the beam projected on the first reflector and the less is thedistance across the open mouth of the slot, adjacent which the reflectedbeam must travel; also the less will be the energy diffused or reflectedback and upward through the slot toward the diaphragm; also the less thereflected beam adjacent the mouth of the slot will become out of phasewith the flank diffusion from the front face of the beam.

Nevertheless, there seem tobe practicalv limits for desirable thinnessat the slot. I believe T know the reasons for these limits, but it willbe sutlicient to say that for waves of the intensity that can begenerated by a phonograph diaphragm, that for a slot as thin as inch togive an area of expanded wave front sufficient for satisfactoryloudness, the slot must be longer than is convenient for phonographcabinets of present day commercial widths. Also, extreme thinness ofslot without sufficient increase in length and width of the expansionconduit seems to result in a shriller quality for the reproduction and atendency to too faithful reproduction of needle noises. On the otherhand, a slot thicker than 2 inches sacrifices quality, apparentlybecause of absorption or dissipation of high frequency waves upon whichquality depends. Moreover, the indefinable instrumental quality impartedby the instrument itself, which for a 1} inch slot may be too sharp orshallow, is,

with the two inch slot, too mufl'led and hollow. The two inch main beamprojected from such a slot will have the forward diffusion from itsfront face at least 2 inches out of phase with the part of the reflectedmain beam which travels in the same direction. I have previouslyexplained that it is bad for the lngh-frequency, short waves, to havethe energies thereof get as much as 2 inches out of phase.

In any event, the remarkable results have been attained with a 1-1- inchby 14 inch expansion conduit having a slot outlet approximately 11}inches by 14 inches and with a 24: inch conduit having a slot outletapproximately 24 inches by 1 inch.

sible and may be of advantage to accentuate i this effect by pinching inthe beam more along the axis where the wave path is'shortest than at thesides where it is longer.

Vhere, as in the preferred form, the wide thin sound beam projected fromthe slot impinges successively-upon two high angle reflectors and isthen permitted guided but wide angle expansion in a vertical direction,care should be taken to keep the dimensions 4 of the throat throughwhich the main beam is finally projected, as narrow as may be withoutchoking the exit of said main beam. In practice I have found that thisdimension, the distance from the bottom reflector to the roof at thenearest point, may be not very much greater, and preferably less thanthe inlet slot from which the primary beam is projected, although thisseems to be partly an energy problem and the desideratum seems to be tohave-the beam fill the throat without choking it. For example, where theslot outlet for the primary beam was 14 inches by 15; inches, this finalthroat was 14 inches by 1%; inches, the results were very good, but thissame reflecting projector with this same 1 1 inches by 1-}, inch throat,gave very good results where the primary slot was graduated down firstto 1 inch expanding conduit then a inch and then 4; inch, the 14 inchdimension of the primary slot and the throat being the same in all fourcases.

The reflecting pro-jector mouth piece seems to be of further advantageas affording a considerable further extension of the air column. Bymeasurement in accordance with the scale on the drawings it will be seenthat the reflection path of the axis of the main beam through thisreflecting projector mouth is about 11 inches, which, added to say 14inches for the lateral expansion part, plus say 12 inches for the tonearm, gives a total air column length of say 37 inches which issuilicient'tophysically contain a quarter inch wave length of very lowfrequency. Moreover, the wide mouth of said projector tends to add acertain virtual or phantom acoustic length to the air column so that itwill be safe to say that the above physical dimensions afford acontrolled virtual air column length for generation of quarter wavesnearly 4: feet long, that is to say, near the next to the lowest "octaveon the piano and below the lowest fundamental frequency of the malehuman voice. Of course when the 24 inches by 24 inches lateral expansionis employed the actual physical length of the air column measured alongthe axis is fully 4 feet.

I find the herein described principle of one-dimension expansion of thewave front is so effective that the total length of the air column fromthe diaphragm to the mouth of the projector may be made short and ofvery low frictional resistance, thus making practicable another featureof my invention which consists in arranging the tone arm outlet at thefront of the phonograph cabinet directly over the projector outlet. Thismakes desirable another feature of my invention which consists inarranging the sound box so that the stylus needle trails toward thevertical axis of the tone arm, on the right hand side of the center of arecord. This makes it convenient for right-hand manipulation of thesound box to renew the needle or rotate the same into and out ofoperating relation to the record. A further feature is mounting thesound box upon ball bearings, for rotation about an axis which coincideswith the axis of the sound outlet of said box.

The above and other features of my invention may be morefully understoodfrom the following description in connection with the accompanyingdrawings, in which Figure 1 is a. vertical section along the centralaxis of the sound amplifier and projector showing diagrammatically thepath of the main beam and also a part of the forward diflusion thereofnear the mouth of the projector.

Fig. '2 is a section at right angles to the plane of Fig. 1 taken alongthe curved and broken line 2-2 on said Fig. 1. indicatingdiagrammatically also the lateral expansion and downward curvature ofthe wave front in this dimension;

Fig. 3 is a detail section showing the mounting of the reproducer on thetone arm Fig. 4: is an elevation partly in section on the line 4-4, Fig.3.

Fig. 5 is a plan view of a modification.

For reasons which will be obvious from the foregoing general descriptionof the invention, these drawings are intended to indicate approximatesizes as well as the pro-- portions of the parts in one desirableembodiment of my invention. The scale for Figs. 1 and 2 is indicated onFig. 2, but Figs.

*3, t and 5 are on a scale twice as large.

in these drawings the invention is shown as applied to a cabinet type ofphonograph. The top 1 carries the motor box 2 driving turn table 3supporting record 4 in operative relation to sound box 5 havingdiaphragm 6 operated by a stylus lever 7 through needle to 6 inches.

expansion projector 11, which opens through "the side 12 of the cabinet.

The diaphragm 6 has its inner face in operative contact through opening13, with the upper end of the air column which extends continuouslythrough said parts 9, 14, 10, and 11 to the outer air.

The diameter of the air column may be say a inch to iinch for the lengthof the tone arm 9, but in the device shown this is enlarged to about 1%inches in the standard 14. Then for the next 14 inches or so through theexpansion chamber, the air'column has a front-to-rear contraction to say1%,- inches, while the lateral widening. in the same distance isapproximately 14 inches. The next 4 inches measured along the axis ofthe main beam, follows the reflection path, and is contained in aportion of the projector which actually measures only about 1-} inchesfrom front to rear. The path of the beam from the second reflection outto the mouth of the proj ector is about 8 inches to 10 inches though theshortest distance to the mouth is say 4 inches This is short as comparedwith lengths of either tone arm or primary expansion conduit. The finalexpansion in the vertical direction is also limited as to angle, beingpreferably between top and bottom walls diverging at angles less than90, preferably about to The horizontal width of the mouth across theface of the cabinet is preferably the same or slightly greater than thatof the slot outlet at 15. Usually it will be found convenient andacoustically desirable to make this dimension about the same as thepractically permissible width of the cabinet.

The entire widening conduit 10, together with the entire reflectingprojector 11 might well be embodied in one integral gray iron castinghaving walls say g inch or more in thickness, but as actuallyconstructed by me and as shown in the drawings, the intermediate widenedsection 10 is made of 16 gauge hard rolled sheet brass the sides beingcut to pattern and soldered at the corners. The transverse section issubstantially rectangular throughout. At the upper end the sheet brassis firmly screwed and brazed toa square bushing 16 which is in turnscrewed to the top 1. At the lower end the slot-like outlet isreinforced by a stiff brass frame member 17 which is in turn screwed tothe top board 18 of the reflecting projector. As will be evident fromFig. 2, particularly, the front and rear walls of the widening section10 are of very considerable area and the sheet brass employed beingrelatively thin,

would be liable to vibration in response to the sound waves.Consequently T have re- Locating these relatively sensitive vibratoryareas in advance of the reflecting projector having relativelyinsensitive walls, seems to result in better reproduction of the higherfrequencies while avoiding all tendency to metallic quality. Theseeffects may be.

modified or eliminated, by embedding the vibratory areas or the entireconduit in a plaster of Paris or concrete jacket.

When this part of the device is an integral metallic casting, theinterior surface may be continuousand smooth throughout and, if desired,the exterior may be ribbed instead of clamped.

The reflecting projector 11 constituting the secondary expansion elementis made of hard elastic material smoothly finished on the innersurfaces, preferably well seasoned birch about inch to 1 inch or more inthickness. For simplicity in construction the end walls are parallel,cut to the shape shown in Fig. 1 and having secured thereto by manyclosely spaced screws, the boards constituting the rear reflector 24.bottom reflector 25, bottom expansion guide 26, roof guide and reflector27, and the previously mentioned board 18 to which the outlet of theprimary expansion conduit 10 is secured. The angle between reflectors24, 25 is preferably 90 degrees but variations betwedelin 80 degrees and105 degrees have been use I find that well seasoned birch of propervariety is highly desirable for this purpose, since it takes a verysmooth surface and can be readily stained and polished. Acousticallyconsidered, it is extremely stiff and hard while being elastic in thesense that an ivory billiard ball is elastic. Hence it is almostincapable of absorbing any substantial amount of the sound wave energyand, in the thicknesses and widths above described, is substantiallyincapable of being objectionably vibrated thereby. The same rigidconstruction and material may be employed for the widening conduit 10,if desired.

The surfaces, particularly the inner surfaces are stained. polished andvarnished with care and the joints are all sea-led, as indeed are allother cracks or joints of the entire structure.

Some of the acoustical characteristics of the primarv expansion elementof the air column will be evident from Fig. 2 taken in connection withFig.- 1. Fig. 1 shows how this portion of the air column is kept thinfrom front to rear and in this instance actually converging from 1%inches down to 11} inches. Fig. 2 shows how it expands laterally. Theaxial distance down the line a-b, is 14 inches, which is the distancetraversed by the central part of a wave in reaching the slot outlet at15 viathe line ab. The lines o-c and m-d show the diverging lines oftravel of the waves along the edges, and the curved line dc-bcd showsthe downward curvature of a wave which necessarily results fromequal-speed, equal-distance travel of the waves along said lines ab,a--c, ad. For a 14 inch conduit the portions of a wave crest that travelalong the side lines aal, a,d are some 2 inches or 3 inches behind theportions traveling along theaxi al line a7). Thus the successive wavefronts, that is, identical phases of the same wave, cross the slotoutlet at different times and at different angles, as and with theresults heretofore described. For a. 28 inch conduit, the distance ofthis lag will be 4 inches to 6 inches, thus giving for notes an .octavelower, the same phase differences that the 14 inch conduit gives for thehigher octave. As the wave continues its travels its impingement ondifferent portions of the rear reflector 24 will "be non-simultaneousboth as regards the plane of Fig. 2 and also as regards the plane ofFig. 1; also, the angles of impingement will be different, as regardsthe plane of Fig. 2;

similarly with respect tothe second reflection from bottom. reflector25; similarly with respect to the third reflection fromtop reflector 27.

Fig. 1 also makes it easiergto see why front to rear thinness of theslot outlet 15 is a particularly good thing, when employed incombination with a reflecting projector. The more the slot is narrowedand elongated. the less will be the distance which the reflected wavehas to travel across the mouth of the slot from c to f, Fig. 1.h'loreover. the thinner the main sound beam. the more we may safelydecrease the height of the first reflector 24: by raising the secondreflector 25 thus vertically narrowing the throat at gh so that thesound can fill the projector at this point. If the beam is thick, thediffusion 2Tj, 2 impinging on the bottom reflector 25 will be strong andtoo much energy will be thus reflected directly back, up the air column.

In Fig. 1 also the dotted lines and arrows indicate in a suggestivethough more or less inadequate manner the path of the main beam throughthe reflecting projector and also with less degree of completeness someof the forward diffusion'from the front face Zm of the main beam andalso the face n-o. The curved lines m rand 0r represent'the wave frontsof these diffusions. These various sets of lines indicate that the mainbeam and all "of the stronger portions of the forward diffusion, crossthe plane of the mouth of the projector at comparatively hi h angles andat difi'erent'angles and at di erent times. Thus the curvature of thewave front and its non-simultaneous passage of points where backwardreflection might occur exists not only with reference to the dimensionillustrated in Fig. 2, but also with reference to the other dimensionillustrated in Fig. 1..

It will be evident that the remarkable performance of the air columnabove described is contributed to by the characteristic sudden wideningof the wave front in one dimension, to a long thin slot outlet, withoutexpansion in the other dimension; this being followed by even moreabrupt and shorter distance expansion in the other dimension(vertically) which takes place in the reflecting projector; and also soordering the successive cross-sections of the air column, that the soundpressures can substantially fill the cross section; also the curving ofthe wave front so that the crossing of planes of possible backwardreflection'is non-simultaneous, for each wave and is at widely differentbut mostly sharp angles for different portions of the same front (orphase) of the same wave.

The long, straight-line approach of the sound beam to the firstreflector, between substantially parallel walls, seems to parallel thepaths of oscillation of the particles, thus 'ving a sharper moredependable beam or impingement on the refiector.

Furthermore, the preliminary slot expansion followed by the secondaryexpansion in the other dimension and the reflecting projection of thewaves, makes possible the following features of construction which areof-acouStic as well as structural advantage. The tone arm has itsvertical axis at the front of the cabinet, that is, above and near theoutlet of the projector which opens through the side of the cabinet. Thewaves from the tone arm can be carried almost directly downward andwhatever curvature is necessary, as for instance that shown in Fig. 1,is in the direction in which the air column is thin. At the same timethe air column is being expanded in the other dimension, at a high rate.Frictional losses and particularly attenuation of the high frequenciesis very small because the expansion is so free and the distance soshort. By the time the waves reach the reflecti-n projector, the wavefront has been expan ed so thatthe distance and therefore the velocityof oscillation of the air particles in propagating the wave, is greatlydecreased. As friction decreases much more than in direct proportion todecrease of velocities, the frictional losses are much reduced. li'loreover, the propagation of the waves in this part of the air columnbeing by reflection from hard polished surfaces, losses for the higherfrequencies are small.

In my projector the waves, withoutihaving to traverse any curves afterthey have been expanded more than two inches in the direction of thecurve and without having to turn any corners except by high anglereflection, are enabled to traverse an air column which, as we have seenabove, is 36 inches or more in length, yet the main beam emerges fromthe mouth of the projector not more than 8 inches or 10 inches from thebase of the tone arm outlet.

The thus compactly disposed air column adords the desired quarter wavelength column for the generation of the long waves of the lowestfrequencies newssary for phonograph work, and at the same time, affordsa low friction, phase-preserving path for the high frequencies uponwhich the quality of the reproduced sound depends.

The novel location of the tone arm on the same side of the cabinetthrough which the sound is projected into the outer air, would require atone arm and sound box of usual construction, to trail on the left-handside of the record which would be awkward and inconvenient in practice.Ac cordingly my invention includes arrangin the sound box to operate onthe right han side of the record with the stylus trailing toward thevertical axis of the tone arm. The preferred construction for thispurpose is illustrated in Figs. 1 and 2. The tone arm 9 is curved aroundthrough a right angle to form a horizontal terminal portion 29. (in thisis mounted a housin 30 in which may be fitted an ordinary, read-assembled roller bearing comprising outer ring member 31, theintermediate balls 32 and the inner ring member 33. The latter hasfitted within the same a relatively long sleeve 33', on the outer end ofwhich the sound box is secured by means of screw 34:. A face plate 35closes in and protects the ball race. Outside of the housing 30 issecured a spring 36 adapted to frictionally engage and retain the soundbox when turned to the uppermost position for removal or insertion ofthe needle or for discontinuing operation of the phonograph. The weightof the projection 37 and housing 38 on the sound box maybe adjusted. tocause the stylus to bear upon the record with any desired degree offorce. While this mounting for the sound box is of special advantage inconnection with my present invention it is obvious that any known ordesired sound box and any known narrate or desired mounting thereof maybe employed.

While characteristics of one illustrative form of a composite aircolumn, and the structure whereby all of the various features arepractically attainable, it will be obvious that the perfect reproductionobtainable by this invention is contributed by and is the compositeresult of numerous very novel features 10- calized at various pointsalong the air column, each of which represents careful study, inventionand discovery by itself, as well as in relation to the whole. F orinstance, it is in the nature of a discovery that where the air columnis expanded in one dimension only, the expansion may be very rapid, provided the other dimension be sufficiently thin; that preferably thisother dimension is less than 2 inches; that when the thinning in of thisdimension gets down toward a half inch and less, the length and width ofwidening conduit required to give the desired enlargement of wave frontmay become great, that is, say 24 inches or even 36 inches for a inchslot, and that the limitations on slot thicknesses are of particularimportance with reference to the higher frequencies to be reproduced.Another instance is discovery of the desirability for the thinness ofmain sound beam in connection with. a reflecting projector, and thedesirability of narrowing the throat so that the sound may fill thesame. Another instance is the discovery, involving more or less of theforegoing, that the best way to expand a wave is to give it primaryguided expansion in one dimension, keeping the other dimension small,preferably well below 2 inches until expansion in said dimension isadequate, then affording the wave a guided and limited, but neverthelessrapid secondary expansion in planes at right angles to the primaryexpansion.

When ll speak of expansion in one dimension followed by expansion inanother dimension the word dimension is not to be taken in a strictlygeometrical sense, that is to say, it is the spacing and proximity ofthe front and rear walls of conduit 10, that is of importance so far asconcerns the broader aspects of the invention involved. If the spacingand proximity be preserved these Walls could be given a curvature in adirection parallel'with the waves. As an extreme illustration, thedesired proximity of the walls could be preserved where one wall is acone and the other wall an inner cone concentric with the first. In thisparticular case the benefit of a downwardly curving wave front crossingthe mouth of the projector at different distances and times and angles,will be lost unless the mouth of the conduit were cut on a plane at anangle to the axis of the cones This instance is cited T have describedin great detail the s ea I iio

While the vertical end walls of the pro jector mouth are above describedas parallel,

the principal value of this is cheapness of construction. They maydiverge or converge, provided the angle be not too abrupt. With respectto lateral diffusion of the sound, in the outer air, it will be notedthat the 24 inch slot does not sound as loud as the 14 inch slot when infront of the respective instruments, whereas, from an adjoining (side)room, the 14 inch slot will not sound as loud as the 24 inch slot, atleast this is so for many kinds of records.

With respect to the length for conduit 10, it will be noted that if aconduit 14 inches by 14 inches by 1 inch makes the edge pertions of agiven wave front or given wave phase 2 inches or 3 inches behind theaxial portion, when passing the mouth 15, then a conduit 28 inches by 28inches would make this distance 4 inches to 6 inches so that the 28 inchconduit would give the same phase differences for a wave front offrequencies an octave lower than would the 14 inch conduit.

For waves of average phonographic in tensity the area to which theconduit 10 widens the wave front, is preferably between 12 square inchesand 30 square inches, although inferior but fair results have beenobtained with a 14 inch by 14 inch by T}; inch conduit, the outlet areaof which is only 7 square inches. A 24 inch by 24 inch by 1 inch havingan area of 24 inches gave almost as good results as a 16 inch by 16 inchby 1% inch which had an area of 20 inches. The latter is perhaps themost satisfactory instrument of all the instruments I have specificallydescribed.

The mouth portion of the projector wherein the thin beam is thickened tothe desired final area is preferably shorter than the axial length ofthe primary conduit and shorter than the width of the beam pro-- jectedtherefrom.

' Fig. 5 shows a tone arm which is bent horizontally in reverse curves,so as to bring the vertical plane of the trailing st lus needle into thesame plane with the vertical pivotal axis of the tone arm. Thefrictional drag of the record on the needle is made to take effect inthe plane of the vertical axis and there is less tendency for the needleto jump the groove in the record or to press more strongly on one sideof the groove than on the other. In the form shown these reverse curvesresult in increasing the length of the tone arm severel inches, as willbe evident by comparision with the form shown in Fig. 1. Fig. 5 alsoshows an adjustable weight 50 screw threaded on a rod 51 which projectsabove and beyond the stylus, whereby the distance, and resultingleverage of pressure of the stylus on the record, may be regulated asdesired.

My present invention includes some of the features disclosed in my riorapplications, Serial No. 298,846, filed ay 22, 1919, Serial No. 305,601,filed June 20, 1919, Serial No. 380,492, filed May 11, 1920, and SerialNo. 404,859, filed August 20, 1920, but I have elected to limit theclaims of said prior applications to features not disclosed herein andto present herein all generic claims intended to cover broadly thefeatures disclosed in said prior applications whether employed in thesensitive sonorous late combinations to which said prior disc osures aremore specifically directed, or in the non-vibratory wall combinations towhich my present application is more specifically directed. It willtherefore be understood that where the claims do not specify the natureof the walls they may be considered as including cases where the wallsare sensitive or some of them as sensitive and others solid butpreferably all the walls are solid. While I have shown and describedwith considerable precision andprecise dimensions as well as the shapeof one desirable embodiment of my invention, it is to be understood thatcertain of these dimensions may be varied to advantage, as I have hereillustrated.

It will be noted that some of the novel features of organization andarrangement of the parts of the phonograph as shown herein resemblethose disclosed in my rior application Serial N 0. 880,492, filed %\Iay11, 1920, and are substantially identical with those shown in myapplication Serial No. 658,007, filed Aug. 18, 1923, which is a.division of this case. I have elected to present the cabinet structureclaims in said divisional application, the claims of this applicationbeing directed to the novel features of amplifier and projector.

I have illustrated-herein and have elected to claim specifically hereinan embodiment of my invention in which the widening conduit has sprinmetal walls adapted to add a brilliant quality to the reproduced sounds.I have also described heavy stiff walls for said widening conduit butspecific claims for the latter modification are necessarily re servedfor another application copending herewith.

My invention is of course independent of my theories with reference toit and in so far as I have stated theories, it has been for the purposeof indicating or accounting for the novel results. Whether correct ornot they will be found useful as hypotheses to assist those skilled inthe art when seeking to apply one or more of my novel principles .to newconditions or purposes.

I claim 2-- 1. The method of amplifying and projecting complex waveshaving high frequency components which method consists in firstexpanding the wave front from an area less than 2 square inches, to awave front at least lat inches in one dimension by less than 2 inches inthe other dimension, While the waves are being propagated a distance notless than 12 inches, then permitting limited guided but rapid expansionof the sheet-like sound wave thus produced, in planes at right angles tosaid first expansion.

2. The method of expanding the wave front of complex sound Waves to agiven area, which method consists in rapidly expanding the beam in onedimension to the required width while maintaining its thickness belowtwo inches and then affording similar rapid expansion in the otherdimenv sion.

3. The method of deflecting sound waves while simultaneously expandingthe wave 7 front to any desired area, which method ineludes confiningexpansion 1n the plane of the desired deflections to less than twoinches while expanding to any desired extent in the other dimension;then deflecting the expanded wave front in the direction of its thinnessby impingement upon an approximately plane reflector.

4. ln apparatus of the class described, means enclosing an air column tobe traversed by low and high frequency waves, said means defining aslender portion of the air column, said slender portion having a crosssection which is less than 1 inch square at the inlet end and whichcontinues to be substantially less than 2 inches square for a distanceof more than twelve inches; said means also defining a laterallyexpanding portion for said air column, said portion continuing for afurther length approximately equal to or greater than the length of saidslender portion and widening to a slot-like outlet having one dimensionsubstantially less than 2 inches and the other dimension substantiallygreater than the length of said slender portion of the air column.

5. A sound amplifying conduit for expanding the wave fronts of complexsound waves to a desired area, said conduit comprising a primaryexpansion portion having walls arranged to permit guided and limited butrapid expansion of the wave front in one dimension along widely diverginlines substantially to the width of the desired area, and other wallsarranged to guide and confine the waves without substantial expansion inthe other dimension, thereby forming a thin sound beam. with widelydivergent flanks and a deeply curved wave front; and a secondaryexpansion portion or projector having walls arranged to confine anddefiect inward the divergent flanks of said beam without furthersubstantial expansion in said first dimension and other walls divergingat an angle permitting guided and limited but rapid expansion of saidbeam to the desired area in said second dimension.

6. In the combination specified by claim 5, the further feature of aplane reflector in the projector for directing the laterally expandedsound beam. to said diverging walls for expansion in the otherdimension.

7. In the combination specified by claim 5, the further feature ofarranging the parts so that the sound beam is projected along one of thediverging walls of the mouth of the projector.

8. lln the combination specified by claim 5, the further feature ofhaving the projector directed upward so that the emergmg sound. wavesare protected upward and at considerable angles to the plane of themouth of the projector for the purpose described.

9. In the combination specified by claim 5, the further feature ofarranging the parts so that different portions of the front of anemerging wave cross the mouth of the projector at different times, andat sharp angles.

10. lln the combination specified by claim l, the further feature ofarranging the slotlike outlet with different portions of its longerdimension at substantially difierent distances from the inlet so thatdifierent portions of the same wave front must travel substantiallydifferent distances to reach the plane of the outlet, $01 thatsubstantially different phases of the same Wave will cross the plane ofthe outlet at the same time.

11. Means for expanding and projecting waves of all periodicitiesincluding a conduit to be traversed by the wave having two oppositesides less than 2 inches apart for a, distance not less than 12' inchesmeasured along the axis and two other opposite sides diverging to adistance approximately equal to said length as measured along the axis.

12. A sound amplifying conduit having an inlet less than 2 inches squareand an outlet not less than 12 inches widthwise and less than 2 inchescrosswise, the length of the conduit intermediate the inlet and outlet,measured along the axis, being approximately equal to the widthwisedimension of said outlet and the walls between the inlet and outletcomprising two opposite walls less than 2 inches apart and two otherwalls diverging at progressively increasing angles to a maximumdivergence of approximatelyuQO? 13. A sound projector comprising a thinflat expansion conduit, rapidly diverging to great width as comparedwith its thickness, its thickness being less than 2 inches, the conduitbeing curved in the direction of its thinner dimension and discharginginto a shorter conduit having a wide expansion angle in the direction ofsaid thinner dimension.

14. In the combination specified by claim 13, the further feature ofhaving two walls substantially straight and parallel ifor Iaconsiderable distance of its length where it approaches the outlet.

15. A projector having two high angle reflecting surfaces on the same,side of the projector, the second reflector being in receiving relationfor reflection from the first reflector, and means for impinging a thin,wide sound beam, less than 2 inches thick and very wide as compared withits thickness, at a high angle upon the first of said reflectors.

16. In a sound amplifier, a sound reflecting surface and a flat walledexpansion conduit leading thereto, having two opposite approximatelyparallel walls for a considerable distance backward from the re flector,said sound reflecting surface being rigidly secured in fixed angularrelation With the outlet of said expansion conduit. 17 A sound amplifiercomprising a primary expansion conduit leading downward from the tonearm adapted to expand the sound waves rapidly in one dimension Withoutsubstantial expansion in the other dimension to project a relativelywide thin sound beam, in combination with a plane reflector arranged todeflect said sound beam in the direction of itsthinness, and a secondplane reflector in receiving relation to the first reflector andarranged to reflect said sound beam through a further angle in the samedirection.

18.- In the combination specified by claim 17, the further feature of aprojector comprising diverging walls for spreading the reflected beam inthe direction of its thin ness.

. 19. In the combination specified by claim 17, the further feature of asecond high angle reflector in position to give the beam a secondreflection in the same direction as the first.

20. In the combination specified by claim 18, the further feature ofhaving the sound outlet to the diverging walls of substantially the samelength and as thin or thinner than the inlet from which the sound beamis first projected on the reflector.

21. In the combination specified by claim 19, the further feature ofhaving the sound outlet to the diverging walls of substantially the samewidth and as thin or thinner than the inlet from which the sound beam isfirst projected on the reflector.

22. A primary expansion conduit having opposite Walls diverging in onedimension much more than in the otherdimension to project a relativelythin sound beam, in

combination with a rojector having two adjacent approximate y planereflectors at a high angle to one another on the same side of theprojector.

23. An amplifier comprising a primary expansion conduit having oppositewalls diverging in one dimension more than in the other dimension toproject a relatively thin sound beam and a secondary conduit having areflecting wall at a high angle to the waves projected through saidconduit and arranged to reflect them in the direction of their thinness;.and a second reflecting Wall on the same side of the projector adjacentand at a high angle to said first mentioned reflecting wall, to reflecta second time in the same direction the waves reflected from said firstmentioned wall. v

24. An amplifier comprising a primary expansion conduit having oppositewalls diverging in one dimension more than in the other dimension toroject a relatively thin sound beam, in com )ination with a secondaryconduit having at least three successive reflecting walls, each arrangedto reflect said projected sound beam in the direction of its thinness,the first of said reflecting walls being at an angle of 45 to the axisof said projected sound beam, the second being adjacent the first on thesame side of the conduit and approximately at a right angle thereto andthe third being in receiving relation to the second but on the oppositeside of the conduit.

25. The method of expanding to the desired area the wave fronts of waveshaving slight divergence, as a preliminary to projecting them into theouter air, which method consists in afl'ording guided, limited expansivedivergence to an angle of 60 degrees or more in one dimension,substantially without expansive divergence in the other dimension, andthen affording guided, limited expansive divergence to an angle ofapproximately 60 degrees or more in said other dimension.

26. The method of expanding the wave front of complex sound waves to agiven area, which method consists in expanding and diverging the beam inone dimension to an angle approximately 60 degrees or more and to therequired width without substantial divergence in the other dimensions,and afl'ording limited guided rapid expansion in the other dimension toan angle approximating 60 degrees or more.

27. The method of deflecting sound waves while simultaneously expandingand diverging the wave front to any desired area, which method includespreventing expan sion in the plane of the desired deflections whileexpanding to an angle of approxiill Gil

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mately 60 degrees or more in the other dimension.

28. ln apparatus of the class described, means embodying an air columnto be traversed by low and high frequency waves, said means defining aslender portion for the air column, said slender portion having a crosssection which is less than 1 inch square at the inlet end and which issubstantially less than 2 inches square at the outlet, said means alsodefining a laterally expanding portion for said air column, said portioncontinuin tor a further length approximately equa to or greater than thelength of said slender portion and widening to a slot-like outlet havingone dimension substantially less than 2 inches and the other dimensionsubstantially greater than the length of said slender portion of the aircolumn; and a projector afiording a further extension of the laterallyexpanded air column continuing for a further length which is less thanthe length or said widened portion, said projector embodying wallsdivergin in directions permitting guided and limited but rapid expansionin planes at right angles to the direction of said lateral expansion.

29. ln apparatus of the class described, means enclosing an air columnto be traversed by high and low frequency waves said means including atone arm defining a slender portion for the air column, in combinationwith a conduit communicating directly with the outlet of the tone arm,and

shaped so as to expand the waves in one dimension only to a wide thinbeam in a length at least as great as the length of said tone arm.

30. lo apparatus of the class described, means enclosing an air columnto be traversed by high and low frequency waves said means including atone arm defining a slender portion for the air column, in combina-.

tion with a conduit communicating directly with the outlet of the tonearm, said conduit having its walls shaped so as to expand the waves to awide thincross section, the width of which is several times thethickness.

3i. in combination with the parts specified by claim 80, two high anglereflectors arranged to deflect said beam twice in the direction of itsthinner dimensions.

32. In the combination specified by claim 31, the further feature ofhaving the wider walls of said conduit approximately parallel for aconsiderable distance back "from the outlet thereof.

33. in apparatus of the class described, a conduit enclosing an aircolumn to be traversed by high and low frequency waves, said conduithaving walls which are characteristically diderent tor three successiveportions of the length or"? said conduit, namenarrate ly, a tubularportion having relatively rigid insensitive walls defining a slender aircolumn, an intermediate expansion portion having two oppositeapproximately parallel walls and two other opposite widely divergentwalls and a projector portion having relatively rigid insensitive wallsincluding two opposite walls which are widely divergent to afford rapidexpansion of the waves in a direction at right angles to the divergentwalls of said intermediate portion.

3a. ln the combination specified by claim 33, the further feature ofarranging the walls of the intermediate portion to afford wide ilatareas capable of slight sympathetic vibration for a wide range of hightrequencies.

35. In the combination specified by claim 3%, the further feature ofhavin the approximately parallel walls of sai lllli'illl'lb diateportion consisting of spring metal in combination with means fordetermining diverging nodal lines for said areas,

36. ln the combination specified by claim 35, the lumber feature oimeans :lor apply ing a transverse pressure along said nodal lines totension the adjacent portions oi the spring metal walls.

37. A projecting amplifier comprising a conduit having an outlet ofrectangular cross section and said amplifier having at least twoadjacent successive portions olt its walls substantially plane, thefirst plane portion being at an angle oi approximately d5 to the soundwaves projected from said conduit and the second at approximately rightangles to said first planeportion and in position to intercept at anglesof approximately as the waves reflected therefrom,

38. A sound amplifier comprising three successive sections, including aprimary expansion section having opposite walls arranged to aitlorduided but rapid expansion of the wave tront in one demension withoutsubstantial expansion in the other dimension, to project a relativelywide thin sound beam; an intermediate section comprising a reflectorarranged in iediate receiving relation to intercept said beam at a highangle and reflect the same in the direction of its thinness; and asecond re tlector arranged in immediate receiving relation to interceptthe reflected beam at a high angle and re-retlect it in the direction ofits thinness; in combination with a secondary expansion section arrangedto receive the beam "from said intermediate section and to ati'ordguided but rapid expansion of its wave "trout in the direction ot itsthinness without substantial expansion in the other dimension, thethroat where the beam enters the secondary expansion section being outheight not ater than the outlet where it leaves the pretty expatrsion.section.

ill]

39. A sound amplifier comprising three successive sections, including aprimary expansion section having 0 posite walls arranged to affordguided ut rapid expansion of the wave front in one dimension withoutsubstantial expansion in the other dimension, to project a relativelywide thin sound beam; an intermediate section havin walls arranged tointercept and deflect said beam in the direction of its thinness throuhv an angle of approximately 180; in com ination with a secondaryexpansion section arranged to receive the beam from said intermediatesection and to afi'ord guided but rapid ex ansion in the direction ofits thinness wit out substantial expansion in the other dimension, thethroat where the beam enters the secondary expansion section being ofheight not greater than the outlet from the primary expansion section.

Signed at Chicago, in the county of Cook, and State of Illinois, this7th day of July ELWOOD GRISSINGER.

